The present invention relates to a multi-cylinder internal combustion engine with individual port throttles located upstream of intake valves.
In a spark ignition internal combustion engine, pumping loss increases when the engine load is reduced. Without throttling, control of engine load can be realized by variation of intake valve opening period. Variable valve timing is proposed in the publication "SAE Technical Paper Series 880388" entitled "Variable Valve Timing-A Possibility to Control Engine Load without Throttle." In this publication, a rotary side valve is located in the intake port upstream of an intake valve (see FIG. 2d of the above-mentioned publication). In this system, phase of valve timing of the rotary side valve is varied. The size of the port volume is small so that the port pressure recovers to near ambient levels during the intake valve closed period. If the size of the port volume downstream of the rotary side valve is large, a throttle needs to be located upstream of the rotary side valve (see FIG. 9 of the above-mentioned publication). With this throttle, the pressure upstream of the rotary side valve is kept below the ambient levels, thus allowing charge control by the rotary side valve with sacrifice of pumping loss reduction.
The series connection of a rotary side valve with an intake valve is a promising system. However, a disadvantage of this system is derived from the use of the rotary side valve. At idle engine operation, high vacuum is created in the cylinder at the bottom dead center. Thus, the poor tightness of the rotary side valve causes problems with the charge control. Furthermore, mechanical losses due to a mechanism for actuating the rotary side valves will increase. No satisfactory solution is yet found which allows individual cylinder control.
Load control with port throttle is proposed in the publication "SAE Technical Paper Series 890679" entitled "The Effects of Load Control with Port Throttling at Idle-Measurements and Analyses." With port throttling, the pressure in the intake port increases during the intake valve-closed period due to flow past the throttle. The pressure in the port increases to ambient before the valve overlap period so that back flow into the intake system from the cylinder is eliminated. This allows increased valve overlap to be used without increasing the residual mass fraction in the cylinder. The application of this concept to multi-cylinder internal combustion engines with port fuel injection necessitates a precision fit of the throttles in order to reduce cylinder-to-cylinder variability of air flow and air-fuel ratio over the idle and part load range of engine operation.
Laying-open Japanese Utility Model Application 1-61429 discloses a multi-cylinder internal combustion engine wherein a throttle is located upstream of intake ports of cylinders, and an air injection nozzle is arranged for each of the ports to inject a jet of air into the corresponding port in order to suppress back flow into the intake system from the cylinder during the valve overlap period. This air injection is intended to improve idle stability of a multi-cylinder internal combustion engine with increased valve overlap. If the amount of air injected is excessive and inducted into the cylinder during the valve overlap period, the change within the cylinder increases, resulting in an increase in idle speed. Thus, the amount of air injected must be so calibrated as not to result in a considerable increase in idle speed.
Laying-open Japanese Patent Application No. 55-148932 discloses rotary valves located upstream of inlet valves of cylinders, and a mechanism for actuating the rotary valves.
An object of the present invention is to improve a multi-cylinder internal combustion engine such that air flow to each cylinder is controlled to reduce pumping work during the induction process over idle and part load range of engine operation.
A further object of the present invention is to improve a multi-cylinder internal combustion engine such that, with a less complicated mechanism, air flow to each cylinder is controlled to reduce pumping work during the induction process over idle and part load range of engine operation.
A further object of the present invention is to improve a multi-cylinder internal combustion engine such that air flow to each cylinder is controlled to reduce pumping work during the induction process at idle engine operation without any undesirable increase in idle speed.
A further object of the present invention is to improve a multi-cylinder internal combustion such that cylinder-to-cylinder variability of output torque is reduced over idle and part load range of engine operation.